1. Field of the Invention
The present invention generally relates to a dynamic traffic control method and a device for the same, and particularly relates to a dynamic traffic control method and a device for the same for use in a radio network system.
2. Description of the Related Art
A radio network system (RNS) constituting a CDMA mobile communications network includes plural radio base stations (Node B) 10 that terminate radio signals received from mobile terminals (UE: user equipment), radio network controllers (RNCs) 12 that control the base stations 10, and an operations system (OPS) 14, as shown in FIG. 1. The RNCs 12 are connected to a core network 16 having a home location register (HLR) 15.
A system for causing the RNCs 12 to control radio output of each of the radio base stations 10 according to channel utilization rates and traffic volumes of the radio base stations 10 is disclosed in, for example, Patent documents 1-4.
According to a system disclosed in Patent Document 1, if a line utilization rate of a first radio base station exceeds a preset value and if a second base station adjacent to the first radio base station has unused capacity, a radio output of the first radio base station is lowered.
According to a system disclosed in Patent Document 2, if a speech channel utilization rate of a first radio base station is higher than a traffic decentralization activation threshold and if a speech channel utilization rate of a second radio base station adjacent to the first radio base station is lower than the traffic decentralization activation threshold, a radio transmission output of an outgoing control channel of the first radio base station is controlled, i.e., lowered by a transmission output difference D within a range such that the adjacent radio base stations do not lose their overlapping areas in service areas, thereby transferring a part of the traffic of the first base station to the adjacent second radio base station.
According to a system disclosed in Patent Document 3, transmission power of a control channel is reduced if the number of communication channels in use is increased. The transmission power is not changed if the number remains the same, and the transmission power is increased if the number is decreased.
According to a system disclosed in Patent Document 4, if the traffic of a radio base station exceeds a threshold, a transmission output of a radio base station that has the least traffic among nearby radio base stations is increased according to an instruction from a center station.
Patent Documents 5 and 6 disclose a system for changing radio zones by causing an RNC to control the radio output of each radio base station, comprising a main radio base station and a sub radio base station, according to traffic volumes of the radio base stations.
Patent Document 7 discloses a system in which a radio base station monitors a channel utilization rate thereof such that a radio output thereof is controlled by the radio base station itself in place of an RNC.
Patent Document 8 discloses a system in which radio base stations control each other. Specifically, if traffic of a radio base station exceeds a threshold, a control channel signal level of the radio base station is lowered and signal levels of nearby base stations are increased.
Patent Document 1                Japanese Patent Laid-Open Publication No. 57-210739        
Patent Document 2                Japanese Patent Laid-Open Publication No. 5-63635        
Patent Document 3                Japanese Patent Laid-Open Publication No. 6-133351        
Patent Document 4                Japanese Patent Laid-Open Publication No. 9-163443        
Patent Document 5                Japanese Patent Laid-Open Publication No. 10-145842        
Patent Document 6                Japanese Patent Laid-Open Publication No. 4-156116        
Patent Document 7                Japanese Patent Laid-Open Publication No. 6-69860        
Patent Document 8                Japanese Patent Laid-Open Publication No. 9-163435        
A problem with the system disclosed in Patent Document 1 is that the radio output control is not activated until the line utilization rate of the first radio base station exceeds the preset value.
In the system disclosed in Patent Document 2, the control is implemented when the speech channel utilization rate of the adjacent second base station is lower than the threshold rate even if the speech channel utilization rate of the second base station is very close to the threshold. This accelerates traffic increase of the second radio base station, so that nearby radio base stations might experience the same situation. If such a chain reaction expands to other nearby radio base stations, call loss, packet loss, or ATM cell loss is increased in the whole network, resulting in lowering of quality of service.
The system disclosed in Patent Document 3 has a problem in that the transmission power control is implemented regardless of the number of channels and traffic volume. That is, if the number of channels is large, a large workload might be placed on the processing capacity.
In the systems disclosed in Patent Documents 1, 2, and 4, the radio output control is not implemented until the channel utilization rate or the traffic volume exceeds the corresponding threshold. For example, with reference to FIG. 2, if a channel utilization rate or a traffic volume of a first cell exceeds a threshold X2, radio output control is implemented to reduce radio output of the first cell and to increase radio output of an adjacent second cell. The radio output control is stopped when the channel utilization rate or the traffic volume of the first cell falls below a threshold X1.
The threshold X2 is usually set to a value at which congestion occurs. When the channel utilization rate or the traffic volume of the first cell exceeds the threshold X2, radio output control is implemented, so that channel switching operations for handover are performed all at once. This might cause significant but temporary congestion in radio base stations.
Moreover, if a rapid traffic change occurs, the radio output control process might be delayed with respect to the change. As a result, many call losses, packet losses, and ATM losses might be caused by the time the control process is implemented.
A problem with the system disclosed in Patent Documents 5 and 6 is that facility configuration is not efficient. Specifically, each radio base station requires a sub radio base station, although a transmission output of the sub radio base station is stopped or the sub base station is not used during normal operations.
In the systems disclosed in Patent Documents 7 and 8, because the control performed by a base station itself or performed between base stations is local for a whole network, call loss, packet loss and ATM loss might be increased in the whole network, resulting in lowering of quality of service.